The present invention relates to a refrigerating unit which has a plurality of compressors installed in parallel and controls the operation capacity according to the load to be refrigerated, and this refrigerating unit is most suitable to a configuration that includes an inverter-driven compressor and constant-speed compressors.
In refrigerating units incorporating an inverter-driven compressor and constant-speed compressors, it has been known to additionally put the constant-speed compressor into operation and reduce the driving frequency of the inverter-driven compressor when the driving frequency of the inverter-driven compressor has reached the maximum value and the load further increases. In conjunction with this, a method worthy to note here has been disclosed in JP-A-09-273819, in which when switching over the operation from the inverter-driven compressor to the constant-speed compressor, the inverter-driven compressor is brought to a halt for a fixed period of time to decrease the operation time of the inverter-driven compressor to thereby improve the reliability of the inverter-driven compressor.
Since in the prior art mentioned above the driving frequency of the inverter-driven compressor is lowered or the inverter-driven compressor is stopped from operating for a fixed period in response to changes in load, it has been difficult to finely control the operation capacity in response to varying load, and there has been a possibility that the load capacity and the operation capacity become unmatched.
The object of the present invention is to make it possible to finely vary the operation capacity in response to changes in load, enable optimum operation according to load, and thereby achieve a reduction in energy consumption.